Intra individual comparison of unilateral Achilles tendinopathy using B-mode, power Doppler, ultrasound tissue characterization and shear wave elastography.

Background: The asymptomatic side of unilateral Achilles tendinopathy (AT) is used as a reference in ultrasound. However, this procedure has not been evaluated in a comparative analysis using B-mode (B-US), power Doppler (PD-US), ultrasound tissue characterization (UTC) and shear wave elastography (SWE).

Methods: Retrospective cross-sectional study. Tendons were assigned to 3 groups: 1) asymptomatic side of unilateral AT N.=55; 2) symptomatic side of unilateral AT N.=55; and 3) young reference group N.=29. The following parameters were analyzed separately for the insertion and midportion: UTC (echo type I, II, III, IV), B-US (diameter, cross sectional area), PD-US (Öhberg Score) and SWE (SWE 3 mm, SWE area) using a Wilcoxon Test (group 1 vs. 2) and a Kruskal-Wallis Test (group 1 vs. 2 vs. 3).

Results: The Wilcoxon Test making an isolated comparison between group 1 vs. 2 revealed a significant difference for all parameters of B-US, PD-US, UTC and SWE (P<0.001, P=0.042), except for the insertion in UTC. However, in the overall analysis including the reference group, the Kruskal-Wallis Test could only detect a significant difference between group 1 vs. 2 for PD-US (P<0.001). Thus, group 1 and 2 had significantly more pathological parameters in B-US (P<0.001, P=0.027), SWE (P<0.001, P=0.008) and UTC (type I, III, IV P<0.001) in both, insertion and midportion, compared to the reference group.

Conclusions: The asymptomatic side of unilateral AT seems to show subclinical tendons alterations in B-US, SWE and UTC in comparison to a young and healthy control group. The asymptomatic side of unilateral AT especially with detectable neovascularization might be at risk for future symptoms. Further studies must examine whether the asymptomatic side can still serve as a reference for intra individual comparison in clinical evaluation.